High programming bandwidth and low power consumption are desired in memory devices to meet customer requirements. However, as temperature increases, the average power consumption by the memory increases, and, as programming bandwidth increases, the average power consumption by the memory also increases.
FIG. 1 is a graph showing two operating zones of a prior art memory device. In Zone 0 (temperatures between 0° C. and “TempTrip”), the memory array operates at nominal programming bandwidth. In Zone 1 (temperatures greater than “TempTrip”), the memory array shuts down (i.e., the programming bandwidth goes to 0). In operation, a proportional-to-absolute-temperature (PTAT) voltage source is used to generate a temperature-dependent reference voltage with a positive temperature coefficient (Vtemp). This temperature-dependent reference voltage is compared to a temperature-independent reference voltage (Vref), typically a bandgap voltage reference. As shown in FIG. 1, Vtemp is greater than Vref at TempTrip. Accordingly, when Vtemp is greater than Vref, a signal (“Vtrip”) is generated to transition from Zone 0 to Zone 1 (i.e., if (Vtemp>Vref) then Vtrip=high, else Vtrip=low). The precision of the temperature sensing circuit depends on the deviation of Vref and Vtemp from ideal conditions. As shown in FIG. 2, a range of ±3σ of Vref and Vtemp results in a relatively large temperature range in which the transition from one zone to another can occur (i.e., ΔTempTrip(Vref)=(ΔVtemp+ΔVref)/slope(Vtemp)). This relatively large temperature range may be undesirable in applications that require a more precise temperature sensing circuit.
There is a need, therefore, a method and memory device for improving the precision of a temperature-sensor circuit.